The present invention relates, in general, to electronics, and more particularly, to semiconductor structures and methods of forming semiconductor devices.
In the past, the semiconductor industry utilized various methods and structures to form switching power supply controllers that were used to form power supplies that provided a regulated output voltage. One advantageous feature was to limit the output power of the switching power supply in response to the current through the power switch of the power supply. An example of such a configuration was described in U.S. Pat. No. 7,215,107 which issued to Djenguerian et al. on May 8, 2007. There generally was a propagation delay from the time the current reached the desired peak value and the time that the switch was actually turned off in response to the current. This propagation delay resulted in an actual peak current that was greater than the desired peak value. In some embodiments, the current was limited based on the amount of time required for the current to change from a first value to a second value. However, determining the time interval and the rate of change required complex circuitry that increased the cost of the power supply controller. Additionally, it was difficult to accurately determine the time interval which resulted in inaccuracies in the output voltage.
Accordingly, it is desirable to have a power supply controller that more accurately limits the power delivered to load, and that has a lower cost.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are reasonable variances from the ideal goal of exactly as described.